Catheter-based off-axis optical coherence tomography imaging system

ABSTRACT

Catheter-based Optical Coherence Tomography (OCT) systems utilizing an optical fiber that is positioned off-axis of the central longitudinal axis of the catheter have many advantage over catheter-based OCT systems, particularly those having centrally-positioned optical fibers or fibers that rotate independently of the elongate body of the catheter. An OCT system having an off-axis optical fiber for visualizing the inside of a body lumen may be rotated with the body of the elongate catheter, relative to a handle portion. The handle may include a fiber management pathway for the optical fiber that permits the off-axis optical fiber to rotate with the catheter body relative to the handle. The system may also include optical processing elements adapted to prepare and process the OCT image collected by the off-axis catheter systems described herein.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional patent applicationSer. No. 61/222,238, titled “CATHETER FOR INTRALUMINAL CIRCUMFERENTIALIMAGING WITH ROTATION ANGLE AND LONGITUDINAL POSITION ENCODING,” filedon Jul. 1, 2009, and U.S. Provisional patent application Ser. No.61/244,408, titled “CATHETER-BASED OPTICAL COHERENCE TOMOGRAPHY IMAGINGSYSTEM” and filed on Sep. 21, 2009.

This application may also be related to pending U.S. patent applicationSer. No. 12/790,703, titled “OPTICAL COHERENCE TOMOGRAPHY FOR BIOLOGICALIMAGING,” filed on May 28, 2010.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference in their entirety to the sameextent as if each individual publication or patent application wasspecifically and individually indicated to be incorporated by reference.

FIELD OF THE INVENTION

Described herein are imaging catheters. In particular, OCT imagingcatheters, systems, and methods of using them with an off-axis opticalfiber are described herein.

BACKGROUND OF THE INVENTION

Visualization during minimally invasive surgical procedures has longbeen understood to enhance the performance and outcomes of surgicalprocedures. However, successful visualization, particularlyvisualization into a tissue volume, has proven elusive. One promisingcatheter-based visualization technology is optical coherence tomography(OCT). OCT has shown promise as an “ultrasound-like” opticalvisualization method, in which a thickness of the tissue volume may beimaged to reveal internal structures at relatively high resolution.

OCT may be particularly useful in conjunction with a catheter that maytraverse tissues and body lumens and may, in some variations, beconfigured to modify or sample tissue in conjunction with the imaging orguided by the imaging. For example, an OCT imaging catheter may beconfigured as an atherectomy catheter. A significant body of scientificand clinical evidence supports atherectomy as a viable primary oradjunctive therapy prior to stenting for the treatment of occlusivecoronary artery disease. Atherectomy offers a simple mechanicaladvantage over alternative therapies. By removing the majority of plaquemass (debulking) it creates a larger initial lumen and dramaticallyincreases the compliance of the arterial wall. As a result, for example,stent deployment would be greatly enhanced following site preparationwith atherectomy. There are advantages related to the arterial healingresponse. By removing the disease with minimal force applied to thevessel and reducing the plaque burden prior to stent placement, largegains in lumen size can be created with decreased vessel wall injury andlimited elastic recoil. This has been shown to translate into betteracute results and lower restenosis rates.

Physician practice is often to a treat target lesion as if it iscomposed of concentric disease even though intravascular diagnosticdevices have consistently shown significantly eccentric lesions. Thiscircumferential treatment approach virtually ensures that nativearterial wall and potentially healthy vessel will be stressed, stretchedor cut unnecessarily.

Currently available systems are poorly adapted for real-time imaging,particularly for use in catheters including atherectomy catheters. Forexample, much is already known about FORJ technology (Fiber OpticRotating Junction), spinning mirrors, spinning prisms, and motors in thedistal tips of catheters. However, such embodiments take up a lot ofspace, so much so that they may not be practical for use in conjunctionwith a therapeutic embodiment such as an atherectomy device.

It is generally desirable to reduce the crossing profile of the catheterto enable access to distal tortuous vessels in the heart or theperiphery without collateral damage. The invention described here mayachieve these aims. There are no large, expensive, fragile rotatingjunctions or rotating mechanisms in the catheter distal tip. The fiberis terminated in an adhesive that forms a single, unique, well-definedreference reflection with no complicating intermediate reflections. Thedrive shaft can have a small OD (0.012″ demonstrated), minimizing theeffect on crossing profile.

The devices described herein may form a circumferential view using theimaging catheter, allowing a true full circumferential field of viewwith a very small impact on crossing profile while preserving theability to use common-path interferometry. Prior art devices (e.g.,Lightlab™ ImageWire, MGH fiber optic rotating junctions, Cardiospectra(Milner)) generate full circumferential views inside a body lumen eitherby having a fiber rotating junction (e.g.,http://www.princetel.com/product_forj.asp) between the OCT console andthe catheter tip, with spinning of the optical fiber, by having amechanism on the end of the catheter that rotates a mirror or prism, orby wagging the fiber in one or two axes or planes.

A FORJ necessarily introduces a break in the fiber. In this type ofsystem, light goes from being confined in the core of the fiber topropagating in free space and is then re-imaged back into the fiber.See, e.g., Bouma (U.S. Pat. No. 7,382,949). Two problems immediatelyensue from this arrangement. First, the break in the fiber and there-imaging optics create several surfaces with potentially very largereturn losses (back-reflections) compared to the usual OCT referencereflection. This makes the device difficult to use with common-pathinterferometry, as the interferometer will index off the firstsubstantial reflection. One cannot simply make the reference reflectionbrighter than these surfaces, as (a) this would then create a referencereflection that could saturate the detector if it needed to be greaterthan, for example, 20 microWatts, and (b) the strong reflections presentin the proximal optical path could still lead to artifacts in the OCTimage, as these reflective surfaces would still be orders of magnitudebrighter than the signal from the tissue. Second, the alignment of thetwo fiber cores has to be maintained to an exceptionally high tolerance,typically less than 0.5 microns of wobble as the device rotates. Such ahigh level of accuracy drives up the cost of the device significantly,which is something of particular concern in a single-use disposabledevice.

One attempted solution to the internal reflection problem in the FORJ isto have a rotating junction that incorporates index matching fluidbetween the fixed and rotating fiber cores. This solution is not reallysuitable for cost and complexity reasons as a component of aone-time-use disposable catheter. Incorporating the FORJ into thecapital equipment complicates the design of the interface as this nowhas to be a sterilizable multi-use unit resistant to liquid andcontaminant ingress. These requirements may be incompatible with thematerials and assembly techniques used to make the FORJ.

Furthermore, a rotating mechanism on the distal tip significantlyincreases the crossing profile and complexity of the device. It isgenerally unsuitable for use with a single-use disposable device wherecosts must be minimized. In a device intended for small diameter bodylumens, for example coronary arteries, the presence of a large diametermechanism in the distal tip will define the maximum vessel size that canbe safely treated. The mechanism may also increase the rigid length ofthe catheter, which will in turn restrict the vessel tortuosity intowhich the catheter may be safely inserted. This may preclude use of thedevice in the mid- or distal coronary arteries or in the distalperipheral vasculature, for example the dorsalis pedis.

The methods, devices and systems described herein allow intra-luminalcommon-path low-coherence interferometry with a contiguous fiber pathwhile also allowing the creation of and updating of 360° circumferentialviews inside a vessel with angle and longitudinal encoding. Common-pathinterferometry is highly desirable for a catheter, as it eliminates theneed for a separate reference arm and makes operation insensitive tomanufacturing variations in catheter length. The devices, systems andmethods described herein allow for creation of a >360° circumferentialview as well as a 3-D reconstruction or rendition of the traversedtissue volume, without a break in fiber continuity. These methods,devices and system are particularly suitable for directional atherectomyor directional re-entry, as the imaging element can be steered towards aregion of interest and allowed to dwell there so that the cutprogression and depth can be monitored in real time.

There is a need for a method of forming a circumferential image in alumen in a manner that permits the use of common-path interferometry andthat has a minimal impact on crossing profile and work flow in thecatheter lab. Common path interferometry eliminates the down-leadsensitivity that makes catheters for Michelson interferometry verycostly to produce. This is because the catheter length has to be matchedto the reference arm in the console to within a few microns or to withinthe adjustability of the reference arm. Common-path interferometry alsoallows the console to be placed an almost arbitrary distance from thepatient and fluoroscopy equipment. The invention described here achievesthese aims. The fiber is contiguous from console to distal tip, with nobreaks to cause large back-reflections thereby permitting common pathinterferometry.

Furthermore, it would be very useful to provide catheter devices andmethods of using them that permit the off-axis placement of the opticalfiber used to form the OCT image. Off-axis placement of the fiber wouldallow the center (core) of the catheter to be used for passingguidewires, additional manipulators, tissue (including cut tissue),drive trains, or the like. However, optical fibers that are positionedoff-axis within a catheter may be difficult to manipulate in theformation of a 360° image, since it may be necessary to rotate theentire catheter, rather than just the optical fiber, as is commonlydone. Rotation of the entire catheter, including the off-axis opticalfiber, relative to a proximate handle or control may result in tanglingor binding of the optical fiber at the proximal location. This couldultimately lead to degradation of the image quality and a break in theworkflow of the catheter lab environment while the optical fiber isuntangled or managed during a surgical procedure.

The devices and systems described herein typically describecatheter-based, off-axis OCT systems that may address many of the needsand problems described above.

SUMMARY OF THE INVENTION

Described herein are catheters having off-axis optical fibers for OCTimaging, OCT imaging systems having off-axis optical fibers and methodsof using OCT imaging catheters and systems.

The devices and systems described herein may include a catheter having ahandle and a catheter body that is rotatable independently of thecatheter body, and an optical fiber extending along the length of thecatheter body while being radially displaced (off-axis) from thelongitudinal axis (midline) of the catheter body. The optical fiber maybe present in a channel.

For example, described herein are Optical Coherence Tomography (OCT)catheter devices for visualizing a body lumen by rotation of thecatheter and an off-axis optical fiber within the catheter, the devicecomprising: a catheter body having an elongate proximal to distallength; an optical fiber extending the length of the catheter body alonga path that is off-axis of the elongate length of the catheter body; aproximal handle rotationally coupled to the catheter body; and a fibermanagement pathway within the handle configured to allow the off-axisoptical fiber to rotate with the catheter body, relative to the handle.

The catheter body may include a central lumen and/or any appropriatenumber of additional lumens, including off-axis (e.g., axially displacedfrom the central lumen) lumens. In some variations, the catheter bodyincludes a channel for the optical fiber. The channel may be locatedoff-axis of the elongate length of the catheter body.

The catheter devices described herein may also include a rotation knobthat is coupled to the catheter body and is configured to rotate thecatheter body when manipulated. The handle may comprise a limiterconfigured to define the allowable number of rotations of the catheterbody. The limiter may be configured to restrict rotation of the catheterbody to any number of full or fractional revolutions, with the typicalrange in constructed embodiments being between about two to six fullrotations. The limiter may be configured to prevent rotation of thecatheter body more than four full rotations. This may be useful, forexample, in a monorail-type (Rapid exchange) configuration of acatheter, in which it may prevent the guide wire from getting wrappedaround the catheter torque shaft and forming a potentially destructivereaming surface. The limiter may be configured to prevent rotation ofthe catheter body more than five full rotations.

In some variations, the rotation knob is configured to rotate thecatheter body by a ratio of greater than one times the rotation of therotation knob. The rotation knob may be configured to rotate thecatheter body by a ratio of 1:n (knob rotation: catheter body rotation),where n is an arbitrary whole or fractional number. It is possible toconstruct the knob to enable reverse rotation of the catheter body withrespect to the rotation knob (i.e., 1:−n). In practice, the rotationknob has been constructed at ratios of 1:3 and 1:4 with respect to thecatheter body. For example, the rotation knob may be configured torotate the catheter body by a ratio of between about 1.5 and about fivetimes the rotation of the rotation knob; the rotation knob may beconfigured to rotate the catheter body by a ratio of about four timesthe rotation of the rotation knob.

In some variations, the device includes a side-facing port that isoptically coupled to the distal end region of the optical fiber. Theoptical fiber may be fixedly attached to the distal end region of thecatheter. The optical fiber may be only fixedly attached within thecatheter body to the distal end region of the catheter, and is otherwisefree to move longitudinally relative to the elongate length of thecatheter body.

In some variations, the device further includes a rotational encoderconfigured to encode the rotational position of the catheter body. Insome variations, the device may be used in collaboration with a positionsensor subunit/system through which the catheter can be placed to encodethe relative rotational and longitudinal position of the device. Theposition sensor can be of varied operating principles. For example, itmay be optical or capacitive, or consisting of singular or plurality ofsensing elements. More specifically, for example, the position sensorcan be an optical mouse chip or a capacitive fingerprint sensor.

The fiber management pathway may include a helically-arranged channelhaving a plurality of turns. The helically-arranged channel may beconfigured as part of a spool. The spool may be positioned or heldwithin the handle, and may rotate with the catheter body. In somevariations, the fiber management pathway includes a helically-arrangedchannel having a plurality of turns, wherein the channel comprises wallshaving an upper radial height and a lower radial height. For example,the fiber management may be configured so that the fiber does notcontact the upper radial height or the lower radial height of thehelically arranged channel.

In some variations, the fiber management pathway is configured so thatthe fiber does not traverse a bend radius of less than the light leakagebend radius for the optical fiber. For example, the fiber managementpathway may be configured so that the fiber does not traverse a bendradius of less than about a 5 mm bend radius.

Also described herein are Optical Coherence Tomography (OCT) catheterdevices for visualizing a body lumen by rotation of the catheter and anoff-axis optical fiber within the catheter that include: a catheter bodyhaving an elongate proximal to distal length; an optical fiber fixed toa distal end region of the catheter body and extending the length of thecatheter body along a path that is off-axis of the elongate length ofthe catheter body; a proximal handle rotationally coupled to thecatheter body; and a fiber management pathway comprising a helicalchannel within the handle that has a plurality of turns, an upper radialheight and a lower radial height; and a limiter that restricts thenumber of catheter body revolutions, thereby preventing the opticalfiber from exceeding the upper or lower radial heights of the helicalchannel as the catheter body is rotated relative to the handle.

Also described herein are methods of managing an optical fiber foroff-axis rotation of an Optical Coherence Tomography (OCT) system, themethod comprising the steps of: taking an OCT image using an opticalfiber that is fixed to a distal end region of a catheter body and thatextends along the length of the catheter body through an off-axispathway within the catheter body and into a fiber management channelwithin a proximal handle to which the catheter body is rotationallyfixed; and rotating the catheter body relative to the proximal handle sothat the catheter body and optical fiber are simultaneously rotated.

The method may also include the step of limiting the rotation of thecatheter body so that the optical fiber does not traverse a bend radiusof less than the light leakage bend radius for the optical fiber. Forexample, the fiber management pathway may be configured so that theoptical fiber does not traverse a bend radius of less than about a 5 mmbend radius.

The method may also include the step of encoding the rotation of thecatheter relative to the handle.

In some variations, the method also includes the step of permitting thefiber to extend longitudinally within a channel extending off-axis alongthe length of the catheter.

The method may also include the step of limiting the rotation of thecatheter body relative to the handle to a specific number ofrevolutions, for example, between about 2 and about 6 full rotations. Insome variations, the method may limit the rotation of the catheter bodyrelative to the handle to about five full rotations.

The step of rotating may comprise rotating a rotation knob that iscoupled to the handle to rotate the catheter body relative to thehandle. For example, the rotation knob may be configured to rotate thecatheter body by a ratio of 1:n (knob rotation:catheter body rotation),for example, a ratio of greater than one times the rotation of therotation knob. The rotation knob may be configured to rotate thecatheter body by a ratio of 1:4, where about one full clockwise rotationof the knob results in about four full clockwise rotations of thecatheter, or (in some variations) between about 1.5 and about five timesthe rotation of the rotation knob.

Also described herein are methods of managing an optical fiber that ispositioned off-axis of a rotating Optical Coherence Tomography (OCT)system, the method comprising the steps of: taking an OCT image using anoptical fiber that is fixed to a distal end region of a catheter bodyand that extends along the length of the catheter body through anoff-axis pathway within the catheter body and into a fiber managementchannel within a proximal handle to which the catheter body isrotationally coupled, the channel having a plurality of helical turnsand an upper radial height and a lower radial height; and rotating thecatheter body relative to the proximal handle so that the optical fiberwinds/unwinds and expands/contracts within helical turns of the fibermanagement channel between the upper radial height and the lower radialheight as the catheter body is rotated in the clockwise andcounterclockwise directions.

The method may also include the step of limiting the rotation of thecatheter so that the optical fiber does expand/contract (e.g., coil)within the helical turns of the fiber management channel to a heightthat is greater than the upper radial height or less than the lowerradial height.

Also described herein are methods of imaging a body lumen by OpticalCoherence Tomography (OCT) using an elongate OCT catheter having an OCTsensor fixedly attached to a distal portion of the catheter. Thesemethods may include the steps of: rotating the catheter from a proximalregion of the catheter to rotate the OCT sensor at the distal portionwhile acquiring OCT images using the OCT sensor; and determining arotational lag (θ) for the OCT sensor at the distal portion; andproviding one or more OCT images corrected for the rotational lag.

In any of the methods described herein, the catheter may comprise anoptical fiber extending off-axis along the length of the catheter.

The step of rotating the catheter from a proximal region of the cathetermay comprises rotating the catheter at least 360 degrees in a firstrotational direction. In some variations, the step of rotating thecatheter from a proximal region of the catheter comprises acquiring afirst image while rotating the catheter at least 360 degrees in a firstrotational direction and acquiring a second image while rotating thecatheter at least 360 degrees in a second rotational direction. Thus,the step of determining the rotational lag (θ) may comprise comparing anOCT image acquired while rotating in a first rotational direction to anOCT image acquired while rotating in a second rotational direction.

The method may also include storing the rotational lag (θ) determinedfor correction of additional OCT images.

The step of rotating the catheter from the proximal region of thecatheter may comprise rotating the catheter from the proximal regionuntil motion of the distal region is observed and recording the extentof rotation of the distal region of the catheter. In some variations,the step of rotating the catheter from the proximal region of thecatheter comprises rotating the catheter in a first rotational directionand a second rotational direction from the proximal region until motionof the distal region is observed in the first direction and the secondrotational direction and recording the extent of rotation of the distalregion of the catheter in the first rotational direction and the secondrotational directions. For example, the step of determining therotational lag (θ) may comprise determining the difference of theextents of rotation of the distal regions of the catheter in the firstrotational direction and the second rotational directions.

Also described herein are methods of imaging a body lumen by OpticalCoherence Tomography (OCT) using an elongate OCT catheter having acentral axis and an OCT sensor fixedly attached off-axis at a distalportion of the catheter, where the method includes the steps of:rotating the OCT sensor at the distal portion while acquiring OCT imagesusing the OCT sensor; and displaying the OCT images as a toroidalmapping.

The step of displaying the OCT images may comprise determining thetoroidal mapping based on the radial position of the OCT sensor relativeto the catheter central axis of the catheter.

In some variations, the method further comprises correcting radialdistortion in the image by scaling the OCT images. For example, themethod may comprise correcting radial distortion in the image bymultiplying the radial positions of the OCT images by a correctionfactor. In some variations, the method further comprises correctingradial distortion in the image by adding a correction offset to theradial positions of the OCT. In some variations, the method furthercomprises correcting radial distortion in the image by applying amapping table of correction offsets to the radial positions of the OCT.

Also described herein are methods of imaging a body lumen by OpticalCoherence Tomography (OCT) using an elongate OCT catheter having acentral axis and an OCT sensor fixedly attached off-axis at a distalportion of the catheter, the method comprising: acquiring a firstplurality of OCT scan lines using the OCT sensor; point-wise averagingof data in the first plurality of scan lines; transforming the averagedfirst plurality of scan lines by Inverse Fourier Transform; anddisplaying the OCT images as a toroidal mapping.

In some variations, the method of further comprises repeating the stepsof acquiring, point-wise averaging and transforming for multiplepluralities of OCT scan lines, and in some variations, the multiplepluralities of OCT scan lines may be point-wise averaged to post-FFTaverage the OCT image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating one variation of a system includingan OCT catheter with an off-axis optical fiber.

FIGS. 2A and 2B show variations of a handle for an OCT catheterincluding a fiber management pathway allowing rotation of the catheterand optical fiber relative to the catheter handle body.

FIGS. 3A and 3B show one variation of a catheter body including anoff-axis fiber optic.

FIGS. 4A-4D show different views (cross-sectional, front, sideperspective, and exploded views, respectively) of another variation of ahandle including an optical fiber management mechanism.

FIG. 5 illustrates one variation of an optical fiber management regionwithin a handle.

FIGS. 6A-6D show side perspective, side, front, and cross-sectionalviews, respectively of one variation of an optical fiber managementspool that may be used as part of an optical fiber management mechanism.

FIGS. 7A-7D show side perspective, side, front, and cross-sectionalviews, respectively of another variation of an optical fiber managementspool that may be used as part of an optical fiber management mechanism.

FIGS. 8A-11 illustrate one method of determining the dimensions of thespool of the fiber management pathway.

FIGS. 12A-12E illustrate various encoders that may be used with any ofthe catheters and systems described herein.

FIG. 13 illustrates one example of a toroidal (annular) display of anOCT image as described herein.

FIG. 14A shows a transparent view of one example of a catheter handleincluding a motor for rotating the catheter body. FIG. 14B is apartially opened view of another example of a catheter handle includinga motor and a fiber management system.

FIG. 15 illustrates a method of determining the proper orientation of ascan image when the direction of rotation changes.

FIGS. 16A-16B illustrate various methods for showing when phase delaycompensation is occurring.

FIG. 17 shows notes and illustrations overlaid on a sector image.

FIGS. 18A-18B illustrate one method of image distortion correction.

FIG. 19 illustrates an indicator superimposed over the imagecorresponding to a desired tissue depth to be monitored.

FIG. 20A illustrates a normal image and FIG. 20B illustrates the sameimage after applying an aggressive contrast stretch technique to enhancethe image.

FIG. 21 shows the contrast curve used to achieve the contrast stretchedimage of FIG. 20B.

FIG. 22 shows a scan image where the bright layers have beenhighlighted.

FIG. 23 shows a waterfall image superimposed with tag information.

FIG. 24 schematically illustrates one method of determining alag-correction angle, θ.

FIG. 25 schematically illustrates another method of determining alag-correction angle, θ.

FIG. 26 schematically illustrates a method of indicating lag correction.

FIG. 27A-C schematically illustrate various methods for correcting theimage to adjust the scaling.

FIG. 28 schematically illustrates a method for reducing noise by FFTaveraging of the signal(s).

FIG. 29 schematically illustrates one variation of the post-FFTaveraging method.

DETAILED DESCRIPTION OF THE INVENTION

Described herein are OCT catheters and imaging systems using them,including methods for using them to image. In general, an OCT catheteras described herein is a flexible elongate catheter that includes anoptical fiber for OCT imaging that extends the length of the catheter.The pathway taken by the optical fiber is displaced from the centrallongitudinal (proximal-distal) axis of the catheter, and thus may bereferred to as off-axis. The catheter body is typically rotationallycoupled to a handle portion so that the catheter body and the opticalfiber rotate together relative to the handle.

OCT Catheters Having Off-Axis Optical Fibers

FIG. 1 illustrates one variation of an OCT catheter having an off-axisoptical fiber that may form part of an OCT imaging system configured asdescribed herein. In this example, the device includes a catheter 1101having a distal end 1103 that includes a one-dimensional OCT sensor(typically configured as a common-path interferometry device that doesnot require a separate reference arm). The sensor includes an opticalfiber that extends through the length of the catheter and is (in thisexample) attached by an adhesive to the distal end region of thecatheter. The “lens” of the OCT optical fiber is positioned facingoutwards axially from a side of the distal end 1103 region. The hatchedarrow 1121 indicates the imaging pathway (not to scale) from the sensor.The catheter 1101 may have an elongate and flexible catheter body 1105.The device may be configured so that the optical fiber imaging from thedistal end is contained within the elongate body. The distal end of theoptical fiber may be, as mentioned above, connected or fixed relative toa region (e.g., the distal end region) of the catheter, but mayotherwise be unfixed in the body of the catheter. For example, thecatheter may include an off-axis channel in which the optical fiberresides along the length of the catheter body. This channel may belubricated to allow the fiber to slide axially (distal-proximal) as thecatheter body bends or curves. In general, however, the optical fiberextends in a pathway that is radially displaced from the midline of thelongitudinal axis (long axis) of the catheter. The pathway may be in achannel or lumen within the catheter body or it may be within an annularchannel. In some variations, the optical fiber may extend in a straightpath along the length of the catheter body, while in other variations,the optical fiber may extend in a helical or arbitrarily windingpathway, wrapping around the longitudinal axis of the catheter body.

The catheter is connected distally to a handle 1107 located at theproximal end of the device. A control 1109 on the handle 1107 may beused to rotate the catheter body, including the fiber optic that formsthe one-dimensional scanner at the distal end. The control may be arotational or rotary control, such as a wheel or knob. The control maybe geared so that the rotation of the control 1109 has a mechanicaladvantage for rotating the catheter body. The system may be geared sothat there is a 1:2, 1:3, 1:4, 1:5, 1:6, etc. mechanical/rotationaladvantage. For example, a 1:4 rotational advantage means that for everyfull rotation (e.g., 360°) of the control 1109 on the handle, the sensorpasses through four full rotations (e.g., 1440°). Partial rotations ofthe control 1109 are multiplied for increased rotation at the distal end1103 by the sensor. In practice, any ratio for the mechanical advantagebetween 1:1 and about 1:6 may be useful. For example a 1:1 ratio is aslow one may desire for image quality reasons, and a ratio of 6:1 may bean upper limit to avoid loss of tactile feedback. For example when thecatheter gets into a tight lesion, if there is too much mechanicaladvantage tearing may occur.

The distal end of the catheter may be configured as an atherectomydevice and may include one or more tissue-removal elements and controls(not shown). For example, the device may include jaws,thermal/electrical/optical ablation devices, or the like, for removal ofmaterial from the vessel. The control for such elements may bepositioned on the handle 1107. Rotation of the sensor may also rotatethe tissue-removal elements.

The control 1109 controlling rotation of the one-dimensional sensor(rotational control) may be any appropriate control, including a dial,knob, button, etc. The handle may be configured to be hand held,although it may be configured to be operated by one- or two-hands. Thehandle may be configured to be held by a peripheral device. In somevariations the control is configured to be operated by one or morefingers of the hand holding the handle. The handle may also includeadditional sensors, including an encoder for determining rotation orrotational position of the controller, as described in greater detailbelow.

The system may also include a connection to a controller 1111 forcontrolling the sensor, including applying power and receiving inputfrom the sensor. The controller may be configured to perform the OCTimage processing and to ultimately display one or more imagesrepresenting the OCT images. The controller may also receive input fromthe encoder or other sensor on the handle. The OCT light source and anyother OCT elements may also be included and/or connected to thecontroller 1111.

In some variations one or more additional input devices (not shown inFIG. 11) may also be used to communicate user commands/input to thecontroller 1111 and/or catheter 1101. An input device (or controllerinput device) may be a keyboard, keypad, joystick, mouse, etc. and mayallow input of commands or selection of options to the system (orpresented by the system) for controlling operation of the system. Forexample, the input device may allow the user to outline/markup regionsof interest (e.g., using a mouse, pen, keyboard, etc.), or to toggleon/off recording/memory or determine parameters (including calibrationparameters) of the system.

The system may also include one or more displays or monitors 1113 fordisplaying the imaging.

In some variations, the system may also include one or more fluidapplication and/or removal components. For example, the catheter 1101may include one or more ports for connection to a fluid perfusion source1115 (e.g., saline, etc.) during operation. Thus, fluid may be perfusedfrom the proximal end of the device out of the distal end of the device(e.g., across the imaging sensor at the distal end). In some variations,the system may be adapted to remove cut material from the distal end ofthe device (e.g., either via suction, aspiration, or internal storage).

As mentioned above, an imaging system as described herein typicallyincludes an optical fiber forming the OCT sensor element at the distalend of a catheter and a processor coupled to the catheter for processingimaging information received from the scanner and catheter. The cathetercan be an atherectomy catheter with a cutting device. The processor orcontroller 1111 can include image processing software, hardware,firmware, or the like.

The OCT images collected may be displayed in any appropriate manner,including using two or more display modalities. For example, aone-dimensional OCT image may be displayed on a rotational axis bydisplaying as a toroid (e.g., two-dimensional ‘doughnut’ shape), asdescribed in greater detail below. The one-dimensional OCT image datamay also be displayed along a time axis as a waterfall-type display.

Displaying one-dimensional OCT imaging data as a two-dimensionalazimuthal image (OCT data with respective rotational angles) can beproduced by rotating the catheter and displaying the one-dimensionalscans using angular information from the proximal end of the catheter.This rotational image is typically a toroid or doughnut-type display andmay emphasize the relative rotational relationship between the differentscans. As described in greater detail below, this display roughlyapproximates a cross-sectional view through the region (e.g., the lumenof a vessel) surrounding the catheter with the one-dimensional scanner.This image may not be scaled; furthermore the orientation of the imagemay not necessarily reflect absolute orientation in the patient.Instead, the orientation may be relative to the location of the scanningOCT imaging pathway.

Exemplary toroidal or azimuthal images are shown in FIGS. 15-20 and 22.The imaging space is the doughnut-shaped area between inner and outercircles. The inner circle may be thought of as the catheter with theoutwardly directed one-dimensional scanner on the outer perimeter. Aline (often shown as colored) extending axially outward from this innercircle represents the relative position of the one-dimensional scannerthat is imaging outward into the surrounding region (e.g., the lumen ofa blood vessel). If the catheter with the one-dimensional scanner (anOCT scanner) is held substantially axially fixed in the lumen of avessel and rotated, the resulting 2D image may represent an OCT image ofa cross-section through the surrounding vessel, including penetratinginto the vessel walls. The catheter is typically manually rotatable backand forth axially around the vessel.

One of the challenges of manual rotation of these catheters is thatthere may be a substantial lag between the rotation applied (e.g., atthe proximal end by the user) and the actual rotation of the distal endof the catheter where the one-dimensional imaging system (optical fiber)imaging pathway extends from the catheter. This problem is addressed ingreater detail below.

As mentioned briefly above, images from the catheter may also bedisplayed on a time axis, separately from the angular rotation axisgiven by the toroidal, azimuthal images just described. Thus, imagesrelating to time and tissue depth can be produced without the angularinformation; these images may be referred to herein as “waterfall”images. These may also be referred to (per ultrasound nomenclature) asM-mode images (e.g., depth vs. time). Both azimuthal and waterfallimages can be displayed simultaneously on a visual display or displays,providing users with information about both the relative position andrelative depth of structures related to the one-dimensional scanner.Thus, a display may include both azimuthal and waterfall images of theone-dimensional scanner. The relative importance of the two modes ofdisplay can be changed in real time to reflect the nature of thesurgical procedure. For example the waterfall or M-mode display is morevaluable during a cutting (atherectomy) operation, whereas the radialdisplay is more useful for pre-treatment survey and planning, andpost-treatment outcome assessment. The switch may be made automaticallywith a control on the device handle, or for example by sensing theactuation of the atherectomy cutter. In some variations the system maytherefore provide a processor for processing and presenting theinformation from the scanner, memory for storing information from thescanner and/or user, one or more computer monitors or television screensfor displaying the images, a graphical user interface (GUI) allowinginteraction with the images, and a control or controller for operatingthe imaging system. Additional elements (some of which are describebelow) may also be included.

For example, a catheter for imaging as described herein can include ahand piece near the proximal end and a controller configured as athumb/finger wheel on the hand piece for controlling rotation of thecatheter during imaging. FIGS. 2A and 2B show variations of handles orhand pieces. Rotation of the finger wheel 202 in the counter-clockwisedirection causes the catheter body (and therefore the OCT imagingelement secured at the distal end region of the catheter) to rotate inthe counter-clockwise direction, and rotation of the finger wheel 202 inthe clockwise direction causes the scanner on the distal end of thecatheter to rotate in the clockwise direction. The finger wheel can alsobe configured to produce opposite rotation of the catheter body (i.e.,clockwise finger wheel rotation producing counter clockwise catheterbody rotation). As discussed briefly above, the finger wheel 202 can beconfigured to rotate the catheter at various gearing ratios, such as ½×(½:1), 2× (1:2), 3× (1:3), 4× (1:4), etc. For example, when the fingerwheel is implemented with a 4× gear ratio, a 90 degree rotation of thefinger wheel translates to a 360 degree rotation of the distal (imaging)end of the catheter.

The catheter body region of the OCT catheter generally is an elongate,flexible and thin body region extending distally from the handle. Thecatheter body is rotationally coupled to the handle. FIGS. 3A and 3Billustrate one variation of a catheter body, showing a cross-sectionthrough the catheter body to indicate the off-axis pathway taken by theoptical fiber forming the OCT image. For example, in FIG. 3A, thecatheter body 301 is an elongate, flexible tube having a central hollowlumen 307 and an off-axis central passage 305 through which an opticalfiber 303 may pass. The optical fiber 303 may terminate distally at awindow (e.g., a side-facing window) 309, from which the optical pathwayforming the OCT image may extend (dashed line). The cut-away region 313of the catheter body in FIG. 3A shows the internal arrangement of theoff-axis pathway 305 for the optical fiber 303, and the center lumen307.

FIG. 3B shows a cross-section through the catheter, also indicating thearrangement of the off-axis pathway 305 for the optical fiber 303, andthe center lumen 307. The catheter body may also include additionalinternal lumens (not shown).

Any appropriate optical fiber (e.g., fiber optic) may be used, includingbend-tolerant fibers (e.g., “bendable” or “bend-loss resistant” fibers).For example, in one variation, the optical fiber has a fiber cut-off ofless than 1240 nm and single mode performance between 1270 and 1380 nm(and be manufactured compatible with SMF-28 standards). The outer jacketof the fiber optic cable may be 2 or 3 mm (OD) polyurethane, forexample. The optical fiber connectors may be Diamond E2108.6 connectorswith a 0.25 dB maximum insertion loss and a −65 dB maximum return loss.Typically, optical fibers have a defined minimum bend radiuscorresponding to the radius below which the signal loss through the wallof the fiber from the fiber core occurs. For example, a highly bend-lossresistant fiber will have a minimum bend radius threshold ofapproximately 5 mm. When the fiber is bent to a curve with a radius lessthan this minimum bend radius, the signal (light) within the fiber willdecrease beyond acceptable levels as light is lost through of the wallof the fiber.

As mentioned, by resisting one end of the optical fiber to the rotatablecatheter body, the optical fiber will rotate with the catheter bodyrelative to the handle. This off-axis rotation of the optical fiber withthe catheter may result in pulling and bending of the optical fiber. Asmentioned above, the signal on the fiber may degrade as the fiber isbent, even in the most bend-tolerant (bend-loss resistant) opticalfibers. Further, the fiber optic may potentially tangle, making thecatheter difficult to use, and may ultimately break if too muchmechanical force is applied.

Thus, the catheter handles described herein may be adapted for handlingthe off-axis rotation and bending of the optical fiber in the catheter.For example, any of the handles described herein may include an opticalfiber management pathway through which the optical fiber extends fromthe rotating catheter body. The optical fiber management pathway may beconfigured so that the fiber does not bend beyond the minimum bendradius of the optical fiber (which may range between 5 mm and 25 mm).For example, the overall fiber management pathway within the handle maytraverse bend radii greater than about 5 mm, greater than about 7.5 mm,greater than 10 mm, etc.

Within the handle, the optical fiber management pathway may include adefined pathway around a spool or drum. For example, the pathway may beconfigured in a helical geometry. Non-helical pathways are alsopossible, and may be used. The spool may include a helical channel thatcurves around an approximately cylindrical body. The channel may havedefining elements (e.g., walls, separated ribs, fins, etc.) extendingfrom a top (e.g., upper radius) to a bottom (e.g., lower radius). Anoptical fiber may pass along this channel in a defined pathway and windaround the spool; within the channel, the turns or windings of the fiberdo not overlap or interact with each other, but are kept separate by thedefining elements of the channel (e.g., walls). As the optical fiber isrotated off-axis, the windings of the fiber may expand or constrictwithin the helical channel (simultaneously unwinding and winding,respectively). The stiffness of the optical fiber will allow the tensionon the fiber to approximately uniformly expand and unwind within thehelical turns around the spool. This is described below, for example inFIG. 5. The dimensions of the channels of the fiber management system,including the size of the spool and the heights of channel walls, forexample, as set by the upper and lower radius, may be calculated toallow a predetermined number of rotations of the catheter (and thus theoff-axis optical fiber).

FIGS. 4A-4D illustrate one variation of a handle including a fibermanagement pathway having a spool. FIG. 4A shows a longitudinalcross-section through a handle, and an exploded view of the handle,showing the component parts of this example, is illustrated in FIG. 4D.FIGS. 4B and 4C show front and side perspective views, respectively. Thecatheter body (including the optical fiber therein) extends from thedistal end of the handle. In FIGS. 4A-4D, the catheter body is notshown, for simplicity. In this example, a nose region may surround thecatheter body, which may rotate therein. The nose may include a supportextension 403 that may also provide strain relief as the catheter bodyattaches to the handle. Proximal to the nose, a rotator assembly 405 mayinclude a control such as a knob (e.g., finger knob 407) that may berotated to rotate the catheter body. The rotator assembly may includingone or more rotation transmission elements, including gears or belts forexample for multiplying the rotation of the rotator knob (e.g., 407) bya multiplying factor (typically greater than 1×, e.g., 1.5×, 2×, 3×, 4×,5×) when rotating the catheter body. The catheter body may be fixed orsecured to a hypotube liner that connects to the catheter body, andprovides an exit (e.g., window) from which the optical fiber may exitthe catheter body and enter the fiber management spool 412. Afterexiting the fiber spool (e.g., the long helically-wound channel of thespool), the fiber may be secured (anchored, fixed, or pinned) to alocation next to or proximal to the spool (e.g., within the handle oroutside of the handle). For example, the fiber may attach to a connectorfor connection to the downstream OCT system (light source, processor,etc.). In some variations, the fiber spool rotates with the catheterbody and may be affixed to a rigid length of hypodermic needle tubing(“hypotube”).

FIGS. 4A and 4D illustrate additional elements that may be included,such as a handle housing (which may include an external grip region)420, a travel or rotation limiter 422, and seals or o-rings 428. Therotation limiter may prevent overturning or rotation of the catheterbody beyond the capacity of the fiber management pathway, i.e., toprevent the fiber from being stressed or placed under tension byover-rotation. In some variations, the rotation limiter may beconsidered part of the fiber management pathway, and may limit therotation of the catheter body to a pre-determined number of rotations(complete rotations clockwise or counterclockwise). For example, thepre-determined number of rotations may be between 2 and 10 (e.g., aboutor less than: 10, 9, 8, 7, 6, 5, 4, 3, etc. including partial rotationsof these such as half, quarter, tenth, etc. rotations). For example, thehandle (e.g., the fiber management and/or rotational control) may beconfigured with a limiter that limits the number of full rotations ofthe catheter body through about 5 complete rotations (1800 degrees ofrotation).

In the variation of the handle shown in FIGS. 4A-4D, the catheter may bean atherectomy catheter or a guidewire-placement catheter that includesa distal end region that is manipulated to cut or move as the device isadvanced or withdrawn. The catheter body (and particularly the distalend region) may also be steerable. Thus, in FIGS. 4A-4D, the distal endmay be manipulated by one or more control elements for steering and/oractuating. The handle may also include one or more ports for theapplication or withdrawal of materials through the catheter (includingperfusion fluid, etc). Exemplary elements are labeled (e.g., slider,rotator, fluid seal tube, luer, etc.) in FIG. 4D.

As described in greater detail below, an encoder 425 may also beincluded to encode the rotational position of the catheter body and/orthe optical window or scanning window near the distal end region of thecatheter body, from which the OCT images are recreated. Any appropriateencoder may be used.

The length of the handle may be varied, as may the width or girth of thehandle. In general, the handle is configured so that it may be easilymanipulated by a single hand, including rotation of the finger knob orwheel. In some variations, the handle may be configured for two hands orbe held by a peripheral device. The variations of the handles shown inFIGS. 2A, 2B and 4A-4D are manual handles, in which the catheter body isrotated manually. In some variations, the catheter body is rotatedautomatically. For example, the catheter body maybe rotated ormanipulated electrically. Thus, the handle may also include a motor ordriver for rotating the handle, and the handle may include controls(e.g., buttons, sliders, etc.) for controlling the rotation.

FIG. 5 shows a schematic of one variation of a fiber management pathway,including a spool 505. In this example, a catheter body 501 includes anoff-axis optical fiber 503. The catheter body is coupled to the spool505, so that the two rotate together, relative to the outer body of thehandle 509. The catheter may include a torque shaft, central lumen, orthe like, as mentioned above. The fiber “take off” from the catheterbody is controlled to ensure that there are no optical losses, and toprevent stress on the fiber that may lead to breakage. For example, thetake off region may be protected by a hypotube liner, as mentionedabove. The catheter body may then be skived at a predetermined windowlocation so that the fiber can exit the catheter and enter the spool ofthe fiber management pathway. The take off region may be configured sothat there are no sharp turns (e.g., all bend radii are greater than thethreshold bend loss radius of the fiber), while allowing the fiber tocoil around the semi-enclosed windings of the spool. In FIG. 5, thespool is shown schematically and forms a helically wound channel withwalls having an upper radius 512 and a lower radius 514. The fiber maycoil around the spool within the channel. As the catheter body andoff-axis optical fiber are rotated relative to the handle, the opticalfiber coiled within the spool may expand (shown as dotted lines) andcontract (shown as solid lines) with clockwise and counterclockwiserotation of the catheter body. A region of the optical fiber proximal tothe spool may be constrained 522 either loosely or tightly so that itmay not move laterally (relative to the handle), while still allowingthe fiber to wind/unwind and expand/contract within the fiber managementspool. Thus, the optical fiber may extend or retract longitudinally asthe catheter body is bent, stretched and/or rotated, by expanding orcontracting the coils of optical fiber within the spool.

The spool of the fiber management pathway may be configured to allow apre-determined number of rotations of the catheter body, and may takeinto account the dimensions of the handle, including the handle lengthand width. FIGS. 8A-11 describe one method of determining the dimensionsof the spool of the fiber management pathway. FIG. 8A illustrates anexemplary helical coil. For any given helical coil, there may be Nrevolutions, the height of each revolution may be H, the distance fromthe helix to the center axis may be r (and the circumference, C, is thus2πr), and the length in one revolution is L, so that N*L is the totallength of the helix. An “unrolled” helix may be represented as shown inFIG. 8B, showing that the unrolled helix becomes a repeating line on aplane, which is the hypotenuse of a right triangle having a base length,C, equal to the circumference of the coil (2πr) and a height of onerevolution of the helix. From this relationship, the total length of thehelix (N*L) can be expressed as: L²=C²+H². Therefore N*L is:NL=N√{square root over (C ² +H ²)}

Application of this relationship to various N and C may be expressed andgraphed as length versus diameter for different numbers of loops, asshown in FIG. 9. By selecting a desired range of rotations (e.g.,between 4 and 5 full rotations), we may use this relationship todetermine the internal and external radii of the helical channels of thespool. For example, in FIG. 10, for four rotations (e.g., 10 to 14 coilsof fiber on the spool), possible dimensions of the spool channel wallsmay be determined by extrapolating values (e.g., drawing straight lines)at different values for the fixed length of the optical fiber located onthe spool, as shown. Extrapolating from line 1 at N=10, the diameter maybe approximately 0.51″, and at N=14, the diameter may be 0.37″ for thesame length of optical fiber. This will therefore suggest a spool withan inner diameter (ID) of less than 0.37″ and an outer diameter (OD) ofgreater than 0.51″. Similarly at line 2, a spool with ID<0.46″ and anOD>0.63″ are suggested.

In practice, some slack must be added back to the spool after a fiber ispulled tight at the higher N_(X) to be used (where N is the number ofwindings that the optical fiber takes on the spool, x is the targetnumber of catheter body rotations, and N_(x)=N+x). FIG. 11 illustratesan example where four rotations are targeted, so the maximum N (N_(X))is 23 and the minimum N is 19. The calculated NL curves versus diameterfor this scenario are shown in FIG. 11. Applying the analysis above, thesuggested OD is 0.75″ and the suggested ID is 0.47″ for the fibermanagement spool. However, in this example it is desirable to add someoptical fiber “slack” back onto the coil, in addition to the necessaryNL. For example, approximately 2.75″ of slack may be added to the spoolafter the fiber is pulled tight at 23 coils. This yields an NL of 36.47″(NL at 0.47″ is 33.99, plus 2.75″). The dimensions for 23 and 19 coilswith a total optical fiber length of 36.74 are therefore anOD(effective) of 0.615″ and an ID(effective) of 0.508″. These effectivediameters for the optical fiber within the helical channel wouldtherefore allow the optical fiber to expand and contract during rotationthrough four turns without hitting either the outer diameter of thechannel or the inner diameter of the spool.

Returning now to FIGS. 6A-7D, two variations of the fiber managementpathway that may be positioned within the handle are shown. In FIGS.6A-6D, the spool is shown including the fiber take off region where thefiber exits the catheter (e.g., a fiber lumen off-axis within thecatheter) and wraps around the spool's helical channel. The centralregion of the spool is left hollow, and may be placed in communicationwith a central passageway of the catheter (and may hold a torque shaft,passageway, etc.). FIG. 6A shows a perspective view of the spool,including a distal region 601 where the fiber exits the catheter bodyand enters the spool channel, and a middle region 603 comprising thespool channel into which the optical fiber is wound. The channel is ahelical winding around the spool, as described above. A proximal region605 includes a rotation limiter region. A pin or other limiter portionmay mate with limiter grooves on the spool, as illustrated in FIG. 6D.

FIGS. 7A-7D shows another variation of a spool having an extended coildesign that may further reduce light loss by avoiding tight radiusbending while providing sufficient knob rotations. For example, comparedto FIGS. 6A-6D, the embodiment shown in FIGS. 7A-7D includes 24 (vs. 15)fiber coils, and has a larger minimum diameter (0.476″ vs. 0.400″) andan increased fiber trench width (0.030″ vs. 0.020″), while the ODremains the same (0.750″±0.001″). The increased number of fiber coilsmay increase the available amount of slack, enabling one more knobrotation (5 vs. 4), and an increased minimum diameter may keep theoptical fiber from being bent too tightly and reduce the amount of lightlost when the fiber is in the tightly wound position. Finally theincreased fiber trench width may make the spool easier to manufacture,and may also allow help prevent binding as the fiber expands andcontracts within the semi-enclosed channel of the spool. The channel isreferred to as semi-enclosed, because the upper surface may be open,though in some variations it may be closed (e.g., within a tube orsleeve). In FIGS. 7A-7D, the rotation stop region 703 has also beenshifted to the distal end of the spool.

As mentioned above, the handle may also include an encoder to encoderotational information about the catheter body and/or the image-formingwindow out of the catheter body. An encoder may provide this rotationalposition information to a processor (including the OCT image processor)for display or calculation of the image based on rotational position.Because a lag may be present between rotation of the distal and proximalends of the device when rotating from the proximal end of the catheterbody, the processor may include logic (including hardware, firmwareand/or software) to correct for the lag. FIGS. 12A-12E illustratedifferent variations of encoders that may be used.

In FIG. 12A, a Hall-effect sensor may be used to detect catheterrotation in the device handle. The rotation can be on- or off-axis. Inthis variation, an encoder gear mates with a gear that is rotated withthe catheter body (in this example, the spool, which is connected to thecatheter body, is rotated). A rotary encoder provides output informationindicating the rotary position of the catheter body.

FIG. 12B illustrates a schematic of a variation having an on-axisthrough-hole encoder. In this example, the rotation of the catheter bodyresults in direct rotation of the encoder. FIG. 12C illustrates oneexample of a non-contact encoder, in which an air gap exists between theencoder sensor and a magnet coupled to the rotary gear that rotates asthe catheter body rotates. The sensor may therefore detect rotation.Similarly, FIG. 12D illustrates another version in which a magnetic ringis attached to the rotatable catheter body/spool. The ring may havebands of opposite polarity alternating around the circumference, inwhich the number of bands is proportional to the angular resolution.Finally, FIG. 12E illustrates another variation, in which there isoptical encoding using a disc attached on-axis to the rotatable catheterbody or a contiguous element (e.g., the spool). An off-axis optical readhead may detect rotation of the disc.

In some variations, the device or a system for using the deviceincorporates a “mouse chip” position sensor similar to those used in acomputer optical mouse in order to look at the catheter and encodeangular and longitudinal motion. Other means of position sensing mayinvolve an element or elements of different operating principles, suchas a capacitive fingerprint sensor.

A mouse chip may look at the surface of the catheter (or the braid ifthe outside laminate is transparent or translucent) and on the basis ofthe difference in feature position between adjacent snap-shots, itcalculates the X and Y motion vectors from which we may deduce rotationand/or longitudinal motion. The features being observed by the mouseimage sensor can be in any shape or form, and the pattern can beregular/periodic or random. Preferably, the features are not perfectlyperiodical at the very least. Most preferably, the features are random.There should be at least one discernible feature within the field ofview of the mouse image sensor within each successive frame.Incorporation of the chip into an access port may allow removal of theoptical encoder from the device, simplifying the device. Alternativelyit may allow compensation for imperfect catheter torque transmission.Rotating the proximal end of the catheter by 360 degrees does notnecessarily lead to a 360 degree rotation at the distal tip,particularly if the catheter is experiencing distributed friction overits length, for example from the introducer sheath, guides, and/ortissue friction especially in a tight lesion. A significant fraction ofthe “wind-up” or “lag” between the rotation of the proximal and distalends of the catheter may come from the unsupported length of catheterbetween the proximal handle and a Touhy-Borst hemostasis valve. Byplacing the mouse chip on the “wet” side of the valve, rotation andlongitudinal motion of the catheter may be detected while eliminatingthe unsupported length effect, thereby increasing the precision ofmeasurement.

The mouse chip output (Z, theta) can be displayed on an image displayand potentially integrated into a fluoroscopy unit display, as describedbelow. Longitudinal data in particular could be used by the surgeon tomeasure the length of a lesion, which would in turn guide the cut on/offpositions.

Preliminary data indicates that lesions in arteries show cleareccentricity, with almost healthy tissue in one or more quadrants of thevessel transitioning into atheroma, lipid rich regions, calcium depositsetc. The data clearly underscore the need for directional therapy. Thus,the catheters described herein may be used for passage throughcardiovascular vessels, and configured to image a wide angle of tissueto millimeter depths, using a single optical fiber configured as acommon-path interferometer in an optical coherence tomography sensor.

Any of the catheters described may be used as part of an OCT systemincluding an off-axis optical fiber within the rotatable catheter body.The system may include any of the elements useful for OCT imaging, suchas the OCT light source, OCT detector(s) and image processors, which mayalso include filtering, signal correction and noise reduction.

In some variations, as mentioned above, the optical fiber may becontained within a passage or lumen of the catheter, which is positionedoff-axis of the longitudinal axis of the catheter body (e.g., radiallydisplaced from the midline of the catheter). For example, the singleoptical fiber may be located in a tube that runs the full length of thedevice. At the distal catheter end, the optical fiber may terminate in afixed solid transparent material of particular refractive index (whichis preferably mis-matched with the refractive index of the optical fibercore in a manner that provides valuable optical properties as describedin U.S. patent application Ser. No. 12/790,703, previously incorporatedby reference). Rotation of the catheter body will rotate the distal endregion where the optical fiber terminates. At the proximal end, thecatheter body can be manually (or automatically) reciprocated/oscillatedto cause the distal end to rotate around an azimuthal angle (includingmultiple complete rotations) while avoiding excessive fiber stress orbend losses and allowing the fiber to be contiguous from the console tothe distal tip (no fiber optic rotating junction is necessary). Theoff-axis rotation of the fiber causes the light beam from the fiber tomove through a well-defined azimuthal angle or complete rotation(s)around the vascular interior. At the proximal end, noise and imageartifacts can be reduced by using a confocal pinhole optical arrangementthat separates the main OCT signal transmitted by the core from anybackground noise transmitted by the cladding. The resulting OCT signalscan be processed to produce panoramic images useful for atherectomy andother applications.

Thus, in some variations, the catheter device for optical coherencetomography (OCT) analysis of a distal target includes: a catheter bodywith a proximal end and a distal end; at least one off-axis opticalfiber configured as a common path interferometer disposed along thelength of the catheter body; at least one fiber unit having a core, aproximal face, a distal face, and cladding, said core and cladding beingcontiguous from the connection at the console to the distal cathetertip, and an optically transparent window near the distal end region towhich the distal end of the fiber is fixed, allowing radiation to emergefrom the tube and impinge on the tissue being imaged at substantiallynormal incidence. A system including these items may also include anoptical radiation source connected at the proximal end of the catheterbody by way of a nonreciprocal element and a processor, which mayinclude an optional OCT background correction unit and a detector.

Any of the systems described herein may enable intravascular imaging todetermine the extent of a disease (e.g., coronary disease) to beassessed in both the azimuthal and longitudinal positions, and may alsoallow the identification of disease states (calcium, lipid, atheroma,fibroatheroma). This may in turn allow the treatment to be planned, anda known depth of cut to be superimposed on the image of the disease.Longitudinal and azimuthal indexing may also allow the physician to makea precise estimate of how long a cut should be, whether to take a secondcut after a first one, whether the cutting embodiment is facing thedisease, and whether the catheter (e.g., cutter) is apposed to thetarget tissue or in physical contact and therefore more likely to make acut. Proximal indexing of longitudinal motion coupled withdisease/non-disease differentiating imaging may allow the precise lengthof cut to be planned and executed. This information may be coupled to anautomated advancement function of the system to ensure that proximalmotion correlates to distal tracking in the vessel and may help preventthe physician from cutting where a cut is not warranted. Directionalimaging may allow the catheter, and specifically variations includingcutters on the catheter, to be accurately aimed at and apposed to thediseased tissue. Directional imaging may also lead to unambiguouscut/no-cut signals that are difficult to make with fluoroscopy guidancealone, which may help reduce procedure times.

High resolution images of vessel wall morphologies may also becorrelated to histologic analysis of excised tissue. This correlationmay enable a real-time histologic review of the disease whilemanipulating the device in the vasculature, which may also make itpossible to target specific disease states. In many of the variations ofOCT imaging catheters described herein, the devices are capable ofresolving an at least 2 mm imaging range that may allow at least onecutter-depths worth of warning of a potential adverse event, for examplea perforation. Imaging may also permit the testing of the optimaldebulking hypothesis, which proposes a correlation between the volume ofdiseased tissue removed from the inner lumen of the blood vessel and thelong term patency of the vessel. Imaging will show precisely how muchtissue has been removed, how much is left, and the treated lumendiameter.

Any of the systems described herein may include an off-axis OCT imagingcatheter including a catheter handle with rotation control, cuttingcontrol, flush control, and angle/position indexing. An OCT catheter mayhave an optical fiber that is fixed at a distal position on the elongatecatheter body (shaft) and the catheter shaft is allowed to rotate withrespect to the proximal handle, although with a well defined number ofturns. The optical fiber travels in an off-axis pathway down the lengthof the rotatable catheter body, and an optical fiber managementmechanism in the handle may prevent the fiber from breaking, bendingbeyond the bend loss threshold, or getting tangled. For example, asingle take-up spool in the handle may be used to permit a set number ofturns before a physical stop is imposed. The catheter handle, includingthe fiber management pathway (one embodiment of which is shown in FIG.5), typically does not require the use of a second take-up spool. Thefiber management system incorporates the fiber on a single internaltake-up spool. The size of the proximal handle is thereforesignificantly reduced, as is the complexity.

Any of the catheter devices described herein may include an encoder inthe proximal mechanism that detects angle and may constantly relay thisinformation to a processor (e.g., computer) controlling the OCT dataacquisition system. The value of the angle may be incorporated into thedisplay algorithm to show a 360 degree view of the inside of the lumen,as illustrated in FIG. 13.

In the image example of FIG. 13, the radial line 1301 denotes thecurrent position of the encoder. The display can be continuallyrefreshed by rotating the catheter in either direction. The wholedisplay can also be rotated and oriented with respect to thefluoroscopic view being acquired simultaneously in the catheter lab. Forexample, the image may be rotated so that the pericardium is “up” or“down” in the image display. By orienting the display and by knowing thespatial relationship between the cutter position and the display (and byimplication, the critical physiological structures in the vessel), thephysician may orient the cutter on the device to cut in a safe manner.In the exemplary display shown in FIG. 13, the image is labeled toindicate exemplary structures that may be distinguished by the OCTcatheter devices and systems, when used in the vasculature. In addition,as described in more detail below, the image indicates the presence andlocation of the catheter relative to the surrounding tissue, resultingin an annular display that may accurately reflect the location andorientation of the catheter relative to the tissue.

As can be seen from the above, having a relatively large catheter insidethe vessel and having the imaging element disposed on the circumferenceof this catheter is advantageous as it brings the imaging element intoclose proximity to the tissue being imaged. There is not a lot of“wasted” imaging distance in the lumen where there would normally beblood. This feature in turn maximizes the imaging range of common pathinterferometry and reduces the volume of blood to be displaced ortrans-illuminated. The catheters in the embodiment have demonstrated anability to “see” through several hundred microns of blood, significantlybetter than contemporary designs. It also enables a representative“size” picture of the internal artery structure to be presented. Thereis little or no NURD—non-uniform rotational distortion—as a result ofthe relatively large torque shaft having excellent torque transmissionproperties. This aspect is crucial for accurate cutter guidance (sizingup lesions in both depth and azimuthal extent).

The imaging and image processing using the off-axis OCT cathetersdescribed above is discussed in greater detail below.

Alternative variations of the catheters described above may include amotor driving the rotation of the catheter body, and/or the advancementof the catheter longitudinally. For example, a controller can beautomated with a motor to drive the rotation of the catheter. Such acontroller may be within the handle, or external to the handle. Amotorized drive may provide a controlled sector sweep of the imagingelement. For example, FIGS. 14A-14B illustrate one variation of a handlehaving a motor.

Part II: OCT Signal Processing

The OCT images collected by the devices and systems may be displayed inany appropriate manner. For example, the OCT images may be displayed asan “azimuthal view” similar to that shown in the example of FIG. 13, oras a “waterfall view” showing linear scanning from the “one dimensional”OCT scanner at the distal end region of the catheter, or both. Althoughin the variations described above the OCT imaging scanner (the end ofthe optical fiber) is shown as near or at the distal end of thecatheter, facing perpendicular to the catheter, the OCT imaging scannermay be positioned at any appropriate region of the catheter, includingmore proximally located positions, and may be oriented moreforward-facing or backward-facing (e.g., at a non-90° angle relative tothe wall of the catheter).

Images from the catheter can be rendered on the display(s) such that theimage remains stationary and a virtual imager position indicates whichdirection the scanner is pointing around the perimeter of the catheter.This method of rendering the image may be intuitive, providing the sensethat the “top” of the image corresponds to the “top” of the vessel orlumen being imaged. In practice, the orientation of the distal end ofthe catheter may be uncorrelated to the actual “top” or “bottom” of thedistal end of the catheter relative to the patient, or it may becorrelated.

As an alternate method of rendering the azimuthal image, the system canmaintain the virtual imager position in one place (i.e. the “top” of thescreen) and rotate the entire image as it is constructed. In a devicewith a coincident imager and cutter, this may have the advantage ofhaving the cutter always in the “up” position. This view is more akin toriding along with the device and seeing what it would see while in thevessel. In some variations, a pseudo image or marked region may indicatethe presence of a cutter or other region or device(s) associated withthe catheter near the imaging region.

In some variations of the systems described herein, additionalpositional or status information on the system may also be displayed inaddition to (or alternatively to) the azimuthal and/or waterfalldisplays of OCT data. For example, in some variations the system mayprovide information on the longitudinal position or movement of thedistal end of the catheter. Movement of the catheter forward/backwardsmay be represented by a representation of OCT data versus axial distance(e.g., forward/backwards) as the device is moved axially. A similaraxial lag (akin to the rotational lag issue mentioned above) may alsoresult, and similar correction methods may be applied.

Lag is a typical problem in rotational catheter system such as thosedescribed here. Since a catheter is not an ideal torque transmittingentity, there will be some phase delay (θ) for which the distal end ofthe catheter does not rotate when the proximal end of the catheter isrotated. This phase delay can cause incorrect orientation of the imagewhen the direction of rotation changes, as well as a smeared sectorwithin the image, and frustration for a user. If the angle θ can bedetermined, however, the system can keep track of the current positionand direction of travel and account for the phase delay when changingdirections. Various methods of determining θ to allow for properorientation of the image will be discussed herein.

One method of determining θ can be referred to as the “overlay” or“side-by-side” mode. In this method, the operator can take one completerotational scan within the vessel or lumen to be imaged, preferably in azone with a visible anatomical feature or fiducial mark. The operatorcan then take a complete rotational scan in the opposite direction atthe same physical location. The processor (e.g., logic, such ashardware, software or firmware) then overlays the two images or presentsthem side-by-side on the display(s). The operator can align the twoimages by rotating the image using the user interface, which shoulddiffer in angle by θ. Once the images are aligned, the software canstore θ and use that transparently in subsequent scans to correct theimage. This method is illustrated in FIG. 15. In FIG. 15, the azimuthaldisplay shows a radially extending line (upper left) indicating theorientation of the sensor. Overlays of the two images (each of which maybe partially transparent with respect to each other) may be manually orautomatically performed. A schematic of this method is outlined in FIG.24.

Another method of correcting for lag uses a fluoroscope or otherreal-time view of the distal end of the catheter as a guide to determinewhen torque has been fully transmitted down the shaft. A schematic ofthis method is outlined in FIG. 25. The catheter body can be rotateduntil motion is seen on the real-time view. The operator (or anautomatic system) can then prepare to determine θ. The catheter body canthen be rotated in the opposing direction until motion is again seen ordetected on the real-time view. In some variations, the operator theninforms the system that the determination is finished. Alternatively,the system may automatically determine this. The difference in angle atthe proximal end from the time the procedure started to the time theoperator ended it is θ.

Yet another method of determining and/or correcting for lag automatesthe procedure by detecting motion from scan to scan. If, for example,the catheter is not rotating due to torque build-up, each single linescan should differ from the next by a small value. Using the differenceof squares method, or other suitable image comparison algorithm, thesystem can distinguish motion from non-motion and hence not update therotational reconstruction of the image while the distal tip is notmoving.

All of the above methods can be accompanied by user interface elementsthat indicate when compensation for θ is occurring. As shown in FIG.16A, an arc can be displayed along the outside of the sector image. Asshown in FIG. 16B, a transparent wedge indicating how much θ remains canbe displayed. These methods may or may not include fading, hysteresis,and other means to remove unnecessary distraction from the user whilestill conveying that windup is being removed instead of active imaging.FIG. 26 show a schematic illustration of this method. The lag correctionmethods described herein are of particular interest in the off-axis OCTcatheters described herein because both the catheter and the opticalfiber (producing the OCT image) are being rotated.

As described above, real time imaging information from the catheter canbe displayed for the operator. In some embodiments, a substantialproportion of interaction with the system is performed by a technician,and the operator (e.g., physician) is most often a consumer of the dataon the display. The technician can annotate the physician's screen imagewith text and/or simple graphics in a non-destructive way that does notdistract from the images on display. FIG. 17 illustrates one example ofnotes and illustrations that can be overlaid onto the image on display.This may allow the technician to highlight regions of interest, such asanatomy, diseases, etc., in real-time, discuss treatment with thephysician, and allow for clearing or storing of the annotations forlater review. This could also be useful for other experts outside thesterile field to interact in a precise graphical way with the operatingphysician.

Because the imaging system described herein is a manual scan device,allowing arbitrary angle positions and sweep ranges, old data maysometime appear on screen if the operator does not scan over previouslyvisited positions. One method for reducing confusion and enhancing thefocus on new data is to gradually fade old on-screen image data basedeither on motion (the more scanning the operator does, the faster theimages fade) or on strict time. This highlights the newest data, as italways appears with maximum brightness and opacity, while allowing theold data to still be visible, but easily distinguished.

Depending on the current activity being performed by the physician (i.e.cutting, rotating, etc.) various portions of the data display havedifferent significance. For example, when cutting it may be moreadvantageous to focus on the “waterfall” (time vs. depth) display. Whentargeting, it can be more useful to focus on the sector (two dimensionalazimuthal) display. Using a variety of sensors, the system can deducethe action and automatically highlight or enlarge the appropriatedisplay for the situation. When cutter actuation is detected thewaterfall portion of the display can be enlarged and the sector displaycan be reduced, for example. These different displays may beadvantageous because they may optimally allow a users own naturaledge-detection to discern features from the otherwise one-dimensionalinformation. In some variations, additional signal processing may alsobe applied to detect or determine features from these OCT images. Forexample, tissue boundaries may be determine or detected, and indicatedon one or more of the displays.

The systems described herein may also automatically or manually togglebetween the one or more display types, or may emphasize one or more ofthe display types. For example, if the system is being used to modifytissue (e.g., cut tissue using an atherectomy element), the waterfalldisplay (which may more easily allow detection of the tissue boundaries)may be enhanced by showing it larger than the azimuthal display, or byshowing just the waterfall display. This may be done automatically ifthe controller indicates that the user will be (or is) using theatherectomy element(s), or it may be done manually before the userselects it.

When displaying the OCT data, the system described herein may correctfor various sources of error. For example, one source of error arisesbecause the sensor (OCT imager) is positioned at the outer edge of arotating catheter. A naïve rendering implementation might draw thesector image from the very center outward (e.g., so that the azimuthaldisplay is more of a circle than a toroid). This depiction would,however, be completely artificial, and result in the features toward thecenter appearing pinched. While this distortion has no impact on theassessment of depth of features, any decisions based on morphology inthe azimuthal direction could be effected by the resultingunderestimation of their size. Since the catheters used herein have aknown diameter and image position, the system can take this into accountwhen rendering by remapping the origin of the polar coordinates to a newradius and scaling the entire image to fit within the field of view ofthe display. This ensures that tissue morphology is correctlyrepresented. FIG. 18A represents an uncorrected image, and FIG. 18Billustrates the same image after correction for the diameter of thecatheter (or radial position of the OCT sensor relative to the cathetercentral axis). In other embodiments, the exact imager position can beencoded into an RFID or other non-volatile memory associated with thecatheter to automate the configuration.

A second source of error may arise in the scanning system. It ispossible that the depth vs. sample number mapping could be nonlinear,resulting in some radial distortion in the image. By characterizing eachsystem at manufacturing time, a mapping of sample number to depth can beconstructed and the system can correct for any non-linearity duringrendering. FIGS. 27A-27C schematically illustrate various methods forcorrecting the image to adjust the scaling as described above.

Overlaying an artificial indicator at a fixed depth from a tissueinterface would enable pre and post-cut depth evaluation, comparison ofnormal healthy tissue morphology to actual image appearance, andpossibly other applications.

As mentioned above, a software approach can be implemented that detectstissue boundaries (and particularly the intimal boundary of a bloodvessel) by searching each scan line for a sharp peak in the firstportion of the scan. Each peak position can be averaged together toreduce noise. Those averaged values can then be added to a fixedconfigurable offset (indicating cutter depth, statistical average mediadepth, etc.) and an indicator can superimposed on the image at that newposition. FIG. 19 illustrates an indicator superimposed over the imagecorresponding to a desired tissue depth to be monitored. It can be seenfrom FIG. 19 that the depth indicator is superimposed on both the sectorscan image (the top image in FIG. 19) and the waterfall image (thebottom image in FIG. 19).

Visualizing the adventitia is one key to a successful outcome in imageguided atherectomy. It can be difficult in some instances to distinguishfrom noise or other layers, depending on image quality. Using imageprocessing techniques, it is possible to enhance the visibility of thelayer structure, making the adventitia easier to pick out.

One method for enhancing the image uses a non-linear contrast stretch to“pull-apart” layers of different reflectivity. The operator can adjustthe mapping of input gray level to output gray level in a way thatemphasizes small differences in intensities. FIG. 20A illustrates anormal image and FIG. 20B illustrates the same image after applying anaggressive contrast stretch technique to enhance the image. FIG. 21shows the contrast curve used to achieve the contrast stretched image ofFIG. 20B.

Another method for enhancing the image attempts to detect the layerstructure directly and overlay or highlight “bright” layers byoverlaying a color or other transparent indicator on the image. Thedifference of Gaussian's approach can be used to find bright layers.Once the image has been processed to find layers, it can be superimposedover the raw image in a new transparent color. FIG. 22 shows an imagewhere the bright layers have been highlighted.

In some embodiments, when an event takes place (such as a capture,cutter activation, lag calibration, etc.) the system can automaticallystore in a meta-data file the time and type of event. In addition, thetag information can be superimposed on the waterfall (time vs. depth)display. This allows real-time marking of disease structure, cut startsand ends, and other events. FIG. 23 shows a waterfall image superimposedwith tag information. As the events are stored on disk, they will appearon the waterfall during playback, providing easier interpretation of thedisplay.

Other methods for improving image quality will now be discussed. Given avery phase stable laser as part of the imaging system, it is possible toaverage several immediately consecutive line scans prior to the inverseFourier transform. Empirical results suggest that this lowers the noisefloor without impacting the signal level. If the laser is not phasestable, or if the lines differ in phase from some other source(high-speed motion, for example), destructive interference may occurwhich could impact the signal level. A mitigation of this effect can beperformed by cross-correlating or otherwise differencing the consecutivelines to evaluate similarity. Lines which differ too greatly from theother in the averaging set could be discarded so as not to impinge onthe final result. The effect of this averaging procedure is to virtuallyincrease the laser power without actually delivering more power to thetissue. FIG. 28 schematically illustrates one variation of a method forreducing noise by FFT averaging of the signal(s).

In an alternative embodiment related to the averaging procedurediscussed above, several of the averaged line results can be bundledtogether and further averaged together after the transform. This has theempirical effect of reducing speckle noise in the image. This procedureis more computationally intense, and may slow the effective scan ratemore dramatically than averaging consecutive line scans alone. Post-FFTaveraging has no requirement for phase stability however, as it isperformed in the intensity domain. High-speed motion may produceblurring, but not destructive interference effects. FIG. 29 outlines onevariation of the post-FFT averaging method described above.

Additional details pertinent to the present invention, includingmaterials and manufacturing techniques, may be employed as within thelevel of those with skill in the relevant art. The same may hold truewith respect to method-based aspects of the invention in terms ofadditional acts commonly or logically employed. Also, it is contemplatedthat any optional feature of the inventive variations described may beset forth and claimed independently, or in combination with any one ormore of the features described herein. Likewise, reference to a singularitem, includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe subject specification, but rather only by the plain meaning of theclaim terms employed.

We claim:
 1. An Optical Coherence Tomography (OCT) catheter device forvisualizing a body lumen by rotation and an off-axis optical fiberwithin the catheter, the device comprising: a catheter body having anelongate proximal to distal length; a central lumen extending in thecenter of the proximal to distal length of the catheter configured topass a guidewire; an optical fiber extending the length of the catheterbody along a path that is off-axis of the elongate length of thecatheter body, wherein a distal end of the optical fiber is fixedlyattached to a distal end region of the catheter, the distal end of theoptical fiber configured to gather circumferential images of the bodylumen as the distal end region of the catheter rotates, and wherein theoptical fiber is otherwise free to move relative to the elongate lengthof the catheter body and configured to actively wrap around the centrallumen during said gathering of the circumferential images as the distalend region of the catheter rotates; and a proximal handle coupled to thecatheter body and configured to control rotation of the optical fiber byrotating the distal end region of the catheter relative to the handle.2. The device of claim 1, wherein the catheter body comprises an opticalfiber channel for the optical fiber, the channel located off-axis of theelongate length of the catheter body.
 3. The device of claim 1, furthercomprising a rotation knob coupled to the catheter body and configuredto be rotated to rotate the optical fiber.
 4. The device of claim 3,wherein the rotation knob is configured to rotate the optical fiber by aratio of greater than one times the rotation of the rotation knob. 5.The device of claim 3, wherein the rotation knob is configured to rotatethe optical fiber by a ratio of between about 1.5 and about five timesthe rotation of the rotation knob.
 6. The device of claim 3, wherein therotation knob is configured to rotate the optical fiber by a ratio ofabout four times the rotation of the rotation knob.
 7. The device ofclaim 1, wherein the handle comprises a limiter configured to limitclockwise rotation of the optical fiber and counterclockwise rotation ofthe optical fiber.
 8. The device of claim 7, wherein the limiter isconfigured to prevent rotation of the optical fiber more than betweenabout two to about six full rotations.
 9. The device of claim 7, whereinthe limiter is configured to prevent rotation of the optical fiber morethan four full rotations.
 10. The device of claim 7, wherein the limiteris configured to prevent rotation of the optical fiber more than fivefull rotations.
 11. The device of claim 1, further comprising aside-facing port optically coupled to a distal end region of the opticalfiber.
 12. The device of claim 1, further comprising a rotationalencoder configured to encode a rotational position of the distal end ofthe optical fiber.
 13. The device of claim 1, wherein the optical fiberis configured in the catheter body so that the optical fiber does nottraverse a bend radius of less than the light leakage minimum bendradius for the optical fiber.
 14. The device of claim 1, wherein theoptical fiber is configured in the catheter body so that the opticalfiber does not traverse a bend radius of less than about 5 mm.
 15. Thedevice of claim 1, wherein the optical fiber is configured to both wraparound and unwrap from the central lumen during said gathering of thecircumferential images.
 16. An Optical Coherence Tomography (OCT)catheter device for imaging a body lumen by rotation and an off-axisoptical fiber within the catheter, the device comprising: a catheterbody having an elongate proximal to distal length and having a rotatabledistal end region; a central lumen extending in the center of theproximal to distal length of the catheter; an annular channel within thecatheter body around the central lumen; an optical fiber fixed to thedistal end region of the catheter body and extending in the annularchannel, wherein the optical fiber is configured to actively wrap aroundthe central lumen during the imaging along a path that is off-axis ofthe elongate length of the catheter body; a proximal handle coupled tothe catheter body and configured to automatically rotate the distal endregion of the catheter; and a limiter preventing the optical fiber fromwrapping around the central lumen more than a set number of timesclockwise and counterclockwise.
 17. The device of claim 16, wherein theoptical fiber is configured to both wrap around and unwrap from thecentral lumen during the imaging.
 18. A method of managing an opticalfiber for off-axis rotation of an Optical Coherence Tomography (OCT)system, the method comprising: inserting a catheter body into a bodylumen, the catheter body having a central lumen extending in the centerof a proximal to distal length of the catheter body; and imaging thebody lumen by taking a circumferential OCT image of the body lumen usingan optical fiber that is fixed to a distal end region of the catheterbody and that extends along the proximal to distal length of thecatheter body through an off-axis pathway within the catheter body,wherein the circumferential OCT image is taken while rotating the distalend region of the catheter relative to a proximal handle so that theoptical fiber wraps around the central lumen of the catheter body duringthe imaging.
 19. The method of claim 18, further comprising limiting therotation of the optical fiber so that the optical fiber does nottraverse a bend radius of less than the light leakage bend radius forthe optical fiber.
 20. The method of claim 18, further comprisinglimiting the rotation of the optical fiber so that the optical fiberdoes not traverse a bend radius of less than about 5 mm.
 21. The methodof claim 18, further comprising encoding the rotation of the opticalfiber.
 22. The method of claim 18, further comprising permitting theoptical fiber to extend longitudinally within an annular channelextending along the length of the catheter around the central lumen. 23.The method of claim 18, further comprising limiting the rotation of theoptical fiber to between about 2 and about 6 full rotations.
 24. Themethod of claim 18, further comprising limiting the rotation of theoptical fiber to less than about 5 full rotations.
 25. The method ofclaim 18, wherein the step of rotating comprises rotating a rotationknob coupled to the handle connected to the catheter body to rotate theoptical fiber.
 26. The method of claim 25, wherein the rotation knob isconfigured to rotate the optical fiber by a ratio of greater than onetimes the rotation of the rotation knob.
 27. The method of claim 25,wherein the rotation knob is configured to rotate the optical fiber by aratio of between about 1.5 and about five times the rotation of therotation knob.
 28. The method of claim 18, wherein the optical fiberboth wraps around and unwraps from the central lumen in the longitudinalaxis of the catheter body during the imaging.
 29. A method of managingan optical fiber for off-axis rotation of an Optical CoherenceTomography (OCT) system, the method comprising: inserting a catheterbody having a central lumen into a body lumen; automatically rotating adistal end region of the catheter body relative to a proximal handle towhich the catheter body is coupled; and imaging the body lumen by takingan OCT image of the body lumen using an optical fiber that is fixed tothe distal end region of the catheter body and that extends along alength of the catheter body through an off-axis helical pathway that isdisplaced from the central lumen within the catheter body and into theproximal handle, wherein the OCT image is taken while rotating thedistal end region relative to the proximal handle such that the opticalfiber wraps around the central lumen during the imaging.
 30. The methodof claim 29, further comprising limiting the rotation of the opticalfiber so that the optical fiber does not coil around the central lumenmore than a predetermined amount.
 31. The method of claim 29, whereinthe OCT image is taken while rotating the distal end region back andforth relative to the proximal handle such that the optical fiber wrapsaround and unwraps from the central lumen during the imaging.